1. Field of the Invention
The present invention relates to a system including a redundant structure and, more particularly, to a redundant system comprising a plurality of systems interconnected in parallel and a selector for selecting an output of any of those systems.
2. Description of the Prior Art
In a switching system of a communication network, interruption of the switching function due to any failure provides a very severe problem. Against this, a dual redundant structure is employed to improve the reliability of the system. In such a dual redundant structure, two systems of the same configuration for performing the same processing are parallel connected (hereinafter, referred to as #0 and #1 systems), and further a redundancy switch is provided for selecting one of the output signals therefrom. Hereby, even if there is detected any failure in one system, the redundancy switch immediately switches to another system to maintain continuity of processing.
Since such a switching system generally switches many signals, it requires the same number of the redundancy switches as that of the signals to ensure input/output operations. Many signals inputted into the switching system are halved respectively and are concurrently fed into the #0 system and the #1 system. Any one of multiple corresponding output signals of the #0 system and the #1 system is selected by the corresponding redundancy switch and is output. Therefore, many complicated signal routes are formed in the #0 system and the #1 system according to the selection condition of the redundant switches.
Referring to FIG. 1, there is illustrated a schematic block diagram showing the simplified structure of a conventional transmission apparatus. As illustrated in the figure, a reception processor 101 receives an input signal and a signal branching portion 102 branches the input signal into two flows to transfer them to two systems of #0 and #1, respectively. The #0 system is comprised of electronic circuit packages 103A and 104A connected in cascade while the #1 system is comprised of electronic circuit packages 103B and 104B connected likewise in cascade. It should be noted that each illustrated circuit package is simplified for description.
A #0 signal and the corresponding #1 signal output respectively from the circuit packages 104A and 104B are selected by the redundancy switch 105, and are output through a transmission processor 106 to the outside. The redundancy switch 105 switches any system to a normal one when any failure is detected as described above.
A selection signal (SEL) indicative of the selection status of the redundancy switch 105 is output to a central controller 107 of the transmission apparatus 1. Actually, the redundancy switch 105 is provided by the number of the signal paths and hence the central controller 107 collects the selection signals from all the redundancy switches in the transmission apparatus 1.
It is assumed that one of the redundancy switches selects the corresponding output signal of the #0 system. The central controller 107 judges from the associated data signal that the signal path of the #0 is at an operational state, and determines that the circuit package 103A of the #0 system is at "operation" while the circuit package 103B of the #1 system is at "non-operation". The operation/non-operation state is stored in an operation information memory ( not shown ) in the central controller 107. The central controller 107 controls operation indication lamps for the circuit packages 103A and 103B which are turned on and off. More specifically, the lamp for the circuit package 103A is turned on when the #0 system at an operational state while the other lamp for the circuit package 103B is turned off when the #1 system at a non-operational state.
It is assumed herein that the redundancy switch 105 is switched over owing to any cause.. The central controller 107 redetermines the circuit package 103A of the #0 system to be at "non-operation" while the circuit package 103B of the #1 system to be at "operation". With the redetermination, the operation information memory in the central controller 107 is updated in its contents, and the operation indication lamp for the circuit package 103A of the #0 system is turned off while the operation indication lamp for the circuit package 103B of the #1 system is turned on. The circuit package 103B, the lamp for which is turned off, is at a non-operation state and hence is made removable for repair or inspection.
However, in the aforementioned conventional system, the central controller 107 collects the selection signals SEL from all redundancy switches 105 at all times and then the operation/non-operation of each circuit package is determined on the basis of the collected selection signals SEL. This causes the central controller to be severely loaded and the processing time from the collection of the selection signals SEL to setting of operation/non-operation is increased. Further, since the central controller controls a lamp for each circuit package, connection lines are needed between the central controller and circuit packages which causes the wiring of the transmission apparatus to be complicated. These difficulties increase as the number of output signals to be processed is increased.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.